1. Field of the Invention
The present invention relates to field of explosive and thermic compositions, in particular to propellants, and more particularly to solid propellants.
2. Description of the Related Art
Solid propellants, that is solid compositions which can rapidly generate gas for propulsion purposes, have a variety of uses. For example, solid propellants are commonly used in rocket motors and in applications such as automotive airbags.
One area of particular interest for the use of solid propellants is closed breech propulsion systems. In closed breech propulsion systems, the propellant gas is generated in a closed chamber to effect the propulsion, rather than being vented as in a rocket motor. Closed breech systems are used, for example, in gun systems, catapults, and aircraft ejections seats.
One aspect of closed breech propulsion systems is that, during gas generation, the pressure of the gas builds in the closed chamber. The gas pressure affects the burn rate of the propellant, and this dependency can be an important operating parameter of the propellant. It is conventional in the art to determine the burn rate of the propellant, typically measured in inches per second (in/sec) as a function of the pressure, typically measured in pounds per square inch (psi). The logarithm of the burn rate of the propellant is typically plotted against the logarithm of the pressure in a burning rate plot, and the slope of such a logxe2x80x94log plot, that is, the change in logarithm of burn rate divided by change in logarithm of pressure, is called the pressure exponent.
A common phenomenon seen with many propellants is a sharp increase in pressure exponent in the region 4000-6000 psi, this increase being known as the xe2x80x9cslope breakxe2x80x9d. This slope break is undesirable in many applications. For example, in aircrew escape systems, such as ejector seats, a closed breech system is used in which the propellant must operate at very high pressures in order to exert a large amount of energy over a short but controlled time frame. The pressure in such systems is strongly affected by the weight of the aircrew member to be ejected, however, and it is desirable to be able to exert less force on lighter pilots than on heavier pilots, so that lighter pilots do not experience excessive G-forces. An ideal system should be able to accommodate a broad range of weights of aircrew members. In order to achieve the desired high pressure and accommodate the range of weights, it is desirable that the slope break be minimized in the useful pressure range.
Another parameter of interest in propellant systems is the temperature sensitivity of the burning rate. This is of particular concern whenever the propellant may be used at a variety of ambient temperatures and a precise control over the burning rate is desirable. Again, this is commonly the case in military applications.
U.S. Pat. No. 3,948,698, to Elrick et al., entitled SOLID PROPELLANT COMPOSITIONS HAVING EPOXY CURED, CARBOXY-TERMINATED RUBBER BINDER, describes propellant compositions having epoxide-cured carboxy terminated rubber and other ingredients including aluminum, ammonium perchlorate, and iron oxide.
U.S. Pat. No. 3,982,975, to Elrick et al., entitled PROPELLANTS HAVING IMPROVED RESISTANCE TO OXIDATIVE HARDENING, describes propellant compositions with components including aluminum, ammonium perchlorate, carboxylated polybutadiene.
U.S. Pat. No. 3,984,265, to Elrick et al., entitled COMPOSITE PROPELLANTS HAVING IMPROVED RESISTANCE TO THERMAL OXIDATION, describes propellant compositions with components including aluminum, ammonium perchlorate, Fe2O3, and carboxylated polybutadiene, a curing agent, and other ingredients including fillers such as carbon black and silica.
U.S. Pat. No. 4,241,661, to Elrick et al., entitled COMPOSITE PROPELLANT WITH SURFACE HAVING IMPROVED STRAIN CAPACITY, describes propellant compositions having components including ammonium perchlorate, aluminum, iron oxide and carboxy terminated polybutadiene, as well as additional agents including an antioxidant.
U.S. Pat. No. 4,375,522, to Braun, entitled THIXOTROPIC RESTRICTOR, CURABLE AT ROOM TEMPERATURE, FOR USE ON SOLID PROPELLANT GRAINS, describes a solid propellant restrictor containing hydroxyl-terminated polybutadiene, carbon black, silica and other ingredients. The restrictor is designed for use in the MK56 rocket motor which employs a solid propellant grain consisting of aluminum, ammonium perchlorate and diisocyanate-cured hydroxyl-terminated polybutadiene.
U.S. Pat. No. 4,882,994, to Veltman et al., entitled PARTICULATE FUEL COMPONENTS FOR SOLID PROPELLANT SYSTEMS, describes a propellant component based on a polybutadiene-styrene latex, which contains aluminum and silica. Propellants using this component and containing ingredients including ammonium perchlorate and hydroxyl-terminated polybutadiene binder are also described.
U.S. Pat. No. 6,086,692, to Hawkins et al., entitled ADVANCED DESIGNS FOR HIGH PRESSURE HIGH PERFORMANCE SOLID PROPELLANT ROCKET MOTORS, discusses solid rocket propellant formulations with a burn rate slope which indicates a substantially insensitive burn rate over a substantial portion of the pressure range. This formulation include ingredients including ammonium perchlorate, a polyalkylene oxide binder, aluminum fuel, ballistic modifier which may be silica, and other components.
Two other compositions currently in use are that used in the M270 impulse cartridge and the CCU22 propellant composition, and their compositions are summarized in Tables 1 and 2. The burn rate profiles of the M270 and CCU22 compositions show substantial slope breaks, however.
It is therefore an object of the present invention to provide an improved solid propellant.
A further object of the invention is to provide an improved propellant for use in closed breech applications.
A yet further object of the invention is to provide a propellant with improved slope break characteristics.
A still further object of the invention is to provide a propellant with lower temperature sensitivity of the burn rate.
Another object of the invention is to provide an improved propellant for use in aircrew escape systems.
These and other objects are provided by the present invention, which includes compositions of matter for use as propellants, methods of making these compositions, and devices incorporating the compositions.
One embodiment of the invention is a composition which includes ammonium perchlorate, iron oxide, finely divided silica and a crosslinkable binder. Another embodiment is a composition which includes ammonium perchlorate, iron oxide, finely divided silica and a crosslinked binder, which may be crosslinked by use of a curing agent. Other components which may be included in the compositions of the invention include powdered carbon, powdered aluminum, plasticizers, bonding agents and antioxidants.